In the past, for a high voltage withstanding display driver (a circuit in which many current outputs are required), a constant-current supply with a circuit structure as shown in FIG. 5 may be considered. As shown in the figure, on the side of a power supply 3 (V.sub.EE), the respective emitters of (high potential withstanding) PNP switching transistors Q.sub.1, Q.sub.2, Q.sub.3 . . . and Q.sub.34 are connected in common, and the bases of the switching transistors Q.sub.1, Q.sub.2, Q.sub.3 . . . and Q.sub.34 are respectively connected to switches 51, 52, 53 . . . and 84. (This circuit diagram shows a state in which the switches are ON, i.e., the state that the base voltage is OV, for example). Collectors of the switching transistors Q.sub.1, Q.sub.2, Q.sub.3 . . . and Q.sub.34 are respectively connected through resistors R.sub.1, R.sub.2, R.sub.3 . . . and R.sub.34 to respective output terminals T.sub.1, T.sub.2, T.sub.3 . . . and T.sub. 34. Each of Z.sub.1, Z.sub.2, Z.sub.3 . . . and Z.sub.34 in the figure represents a load impedance (e.g., picture element of plasma display), and 5 (V.sub.CC) indicates a negative power supply.
Referring to a circuit unit 101 (also to 102, 103 . . . and 134) which are the parts shown by a broken line in this circuit diagram, the resistance value of the resistor R.sub.1 is increased to increase the voltage drop due to the resistor R.sub.1 (assuming that the current flowing R.sub.1 is I.sub.0, R.sub.1.I.sub.0), thereby controlling a change in the power supply 3 and an output current change due to a change in the load impedance Z.sub.1. That is, with a change in the power supply 3 as .DELTA.V.sub.EE, a change in the output voltage V.sub.CC due to a change in the load impedance Z.sub.1 as .DELTA.V.sub.CC, and a change in the load impedance Z.sub.1 as .DELTA.Z.sub.1, we obtain ##EQU1## (where R.sub.1 &gt;&gt;Z.sub.1 +.DELTA.Z.sub.1 ; I.sub.O R.sub.1 &gt;&gt;.DELTA.V.sub.EE ; and I.sub.O R.sub.1 &gt;&gt;.DELTA.V.sub.CC). Therefore, with R.sub.1 as being large (I.sub.O R.sub.1 &gt;&gt;.DELTA.V.sub.EE, I.sub.O R.sub.1 &gt;&gt;.DELTA.V.sub.CC), I.sub.O can be almost constant.
However, in a circuit which requires many current outputs (a power supply circuit having 34 current outputs consisting of circuits 101, 102, 103 . . . and 134 shown by broken lines in FIG. 5), since there are many resistors like R.sub.1 (e.g., 34 resistors R.sub.1, R.sub.2, R.sub.3 . . . and R.sub.34) with large resistance values described above, the voltage drop due to the resistance becomes large, wasting power. There is a problem that this amounts for a large portion of power consumption in the above entire display driver. There is also a problem that it is difficult to form many resistors with large resistance values in a semiconductor IC (integrated circuit) with high precision (without dispersion in the resistance value), (that is, it is difficult to output a constant-current).
An object of the invention is to provide a power supply circuit and a semiconductor integrated circuit device using it wherein power consumption is reduced and dispersion of output current is small.